21.2.1 Comfort and health in buildings

The primary function of buildings is to provide comfortable and healthy environments for its occupants. This is especially important as people spend most of their time either in buildings or inside a vehicle of some sort to get between them.

21.2.2 Materials and waste in eco-design

Generally an ‘eco’ design will use less material or resources which can be measured. The waste that is produced in the production of building material and the eventual disposal of the building is important. The cycle of taking minerals out of the ground to create products, producing pollution in the process and putting them back into the ground when we have finished with them is being challenged. This linear way of doing things is very cheap provided the economic externalities due to the pollution, loss of amenities, or the replacement costs of the resource are not taken into account. However, these other costs and consequences are now being brought to bear in legislation that taxes, limits or bans activities that harm the environment, forcing more benign solutions to be sought.

One way of limiting the use of fresh resources is to create cycles of materials whereby the output and waste of one cycle feeds another, and eventually the loop is closed. This benign view of materials favours products that can be reused as complete elements and then broken down into their component parts and possibly reformed into other complex systems. Glass is a good example of this process, and some cars are now being designed with this in mind. Building elements, however, have not in the past been easy to recycle without considerable labour and energy. It may be that the energy involved in returning a commonly available element into the supply chain is not worth the energy needed to reprocess it. Burning combustible materials to reclaim the energy is one way of dealing with the issue that ignores any of the embedded energy in the manufacture of the material.

Products from the living world do have a ready-made recycling system. Complex structures and processes are generated ultimately from plant life using solar energy, and can be recycled back into the component parts used to build them, namely nutrients, CO₂ and water and can potentially release the energy gathered to make them.

21.2.3 Energy efficiency in buildings

One of the main resources that we are looking to conserve is fossil fuel energy. Putting the carbon that was in the form of gas, oil, and coal from the ground into the air (e.g. as CO₂, CH₄, etc.) is generally acknowledged to be affecting our climate. The fossil fuel resource is finite and as they get more scarce, problems of conflict arise to secure a nation’s supply. Renewable energy sources such as wind, solar, tidal or biomass, etc., will not increase the CO₂ level in the atmosphere. However, compared to fossil fuel it is very capital and labour intensive, which is the reason we made such use of fossil fuels to drive the industrialisation of the last two centuries. Ideally we should be using the cheap fossil fuel as a scaffolding to build the technology to provide the energy we need from renewable energy sources. This is as much driven by a national energy security agenda as a sustainability one. Energy sourced locally from renewable sources reduces one’s reliance on imported energy that could be shut off or exposed to big cost fluctuations driven by world events. Getting agreement on the technical solutions to do this is difficult given the wide range of expertise required, but it is susceptible to analysis by numbers.

The heating, lighting, cooling, ventilating and general powering of buildings are responsible for a substantial proportion of the energy used in the world. In the US it is estimated at 40% (US DOE). This ratio is similar around the world. As such, materials that can reduce the need for energy in a building are a benefit, and would earn the term ‘eco’.

McKinsey & Company have done an assessment of the costs of the various ways of reducing CO₂ production (McKinsey, 2008). On this analysis energy efficiency measures to reduce energy consumption are far more cost effective than generating the power from renewable sources.

David MacKay (2008) has done an excellent job of looking at the whole issue of energy usage and production in the UK, and putting forward a number of models that make the supply and demand add up in a zero fossil fuel economy. MacKay is a physicist and not an expert in any one of these technologies. That is of less importance than the framework he has produced to get the various methods of supply and demand on the same piece of paper using the same units such that they add up. The technologists can then challenge his figures and argue the case on a like-for-like basis. That, however, is simple compared to dealing with the various powerful interest groups, the owners of the existing assets – often the pension funds, subsidy and taxation regimes, planning and regulatory issues.

21.2.4 Food and water

Water and food are linked renewable resources that we rely on that are not infinite. Food requires water to grow and in many areas is the limiting factor in agricultural productivity. As world population grows, strains are put on water supplies which tend to be more local to the user, but food which can travel longer distances can also be a limiting resource. The benefits of using less and gathering the resource locally applies to food and water as it does energy. If a building can use less water and can collect water and grow its own food, it will alleviate the central supply issues in a similar manner to that which a local solar panel does with energy.

21.2.5 Buildings and the external environment

The urban form has historically been hard edged and impermeable using materials such as brick, glass, concrete and asphalt. As such, rainwater is shed very quickly from the surface and into the drains. This has created a problem of overloading the drainage systems, be they man-made pipes and culverts or the natural river systems. This in turn causes flooding, perhaps not at the point of rainfall but some way downstream. The other big loser is the biodiversity and vegetation that cannot live on hard surfaces. Having softer planted areas and retaining the rainwater that falls and allowing it to percolate more slowly into the ground will create more natural habitats for nature and help alleviate the problem of flooding (Anon (b)).

Hard surfaces and the heat from human activity has historically raised the temperature of urban areas above the surrounding planted areas. The ‘urban heat island’ could be considered a bonus when it is cold but not when it is hot. Again, planting on buildings will reduce the temperature of the building surfaces and the cities in general (Alexandri and Jones, 2008),

The countryside is increasingly used for intensive food production using monoculture crops with herbicides and pesticides, which will tend to force out wildlife that does not fit with this land use. As such, urban areas and gardens can provide refuges for wildlife that may have been forced out of the countryside. Buildings that create habitats for biodiversity and retain water are also considered ‘eco’.

21.2.6 Use of space

Humans are also social animals. We have lived in communities that became towns and cities to meet, talk, trade and generally network. Petroleum and cars have allowed us to travel greater distances and live spread apart in low density suburbs. While this provides a sense of space and personal freedom, it uses up a lot of space and fuel, and can lose the social cohesion of the community. Development also tends to reduce the land available for agriculture and nature. Again, while not part of this book, the planning of larger urban areas will have an effect on how sustainable the development is.

21.3.1 Environmental control in a building

The idea of a building is to modify the external climate such that it is more comfortable inside than out. The external conditions like temperature, wind and sunlight vary and by altering the permeability of the building fabric one can moderate the internal environment. However, with the advent of technology and use of energy we can create more or less any internal climate and comfort conditions without reference to the external environment. As we are looking to save energy we are looking to get back to using the passive mechanisms for this environmental control.

21.3.2 Light and daylight

Daylight can be used to displace the need for electric light. The sky is the source of daylight and the greater the view of it the better. Per unit area of glass, a roof light provides more light than a window as it is facing the brightest part of the sky compared to the window that has a more restricted view. Light travels in straight lines and the overall light level in a space is determined by light directly from the source and the diffuse light that has reflected from the surfaces in the room. Daylight does need managing and doesn’t travel very far into a room. The general rule of thumb is that the light will travel 1.5 to 2 times the storey height from the façade into the room. There is a problem with the variation in lighting levels across the room. This is normally dealt with by having most of the windows at the ceiling level and limiting the fenestration below or shading it with a ‘light shelf’. Reflecting the light into the back of the room has been tried on occasion with mixed results. The same issues of variation of light levels applies to artificial light and one tends to mount ceiling mounted light fittings one to two ceiling height apart to give a reasonably even light distribution. The closer the finishes are to white the further the light will penetrate the room.

The sun rises in the east and sets in the west. One needs to be aware of the low direct sun in the morning and afternoon on the east and west façades. However, the further one moves away from the equator, the more the path of the sun varies between summer and winter. In the Arctic Circle, the sun never comes up in mid winter and never goes down in mid summer. This has to be taken into account in designing shading systems. South facing glazing in a northern temperate latitude will benefit from low winter sun to help warm the space. A slight overhang will shade the façade in the summer from the higher summer sun. Any façade that has sun on it will generally need some control over the size or transparency of the opening to prevent glare or overheating. Climates with consistently high daylight levels need smaller areas of fenestration for daylight than duller climates.

From a utilitarian pragmatic point of view, the extent of glazing should be limited to provide enough daylight and no more, to limit the extent of overheating and heat loss. Light is a subset of electromagnetic radiation which in itself is a subset of the different forms of energy. Not all the energy from an electric light is radiation; some is heat lost through convection from the heat generated from the gear and warm lamps. However, all energy be it from electricity or radiation will eventually get degraded into heat. The energy becomes less useful but does not get lost. From a cooling perspective the light directly from the sun has less heat in it than a fluorescent light. The brightest light levels from the sun are about 100 000 lumen/m² with a heat flux of 1000 w/m² giving a rating of 100 lumen per watt. Selective coatings on glass can take out the invisible infrared and UV and increase the relative light to heat ratio. Pilkington Suncool 6 mm 70/35 will let through 69% of the daylight and 37% of the radiant heat. The light to heat ratio will go up to 100 × 69/37 = 186 lumen per thermal watt. By contrast a reasonable fluorescent lamp will provide 68 lumen per circuit watt, going up to 90 for a high frequency ballast T5 lamp running at 35 °C (Osram lighting data). However, while the sunlight may be more efficient than a fluorescent light, it is much more difficult to control.

The fenestration also provides a view especially in tall buildings, with the drama of looking down. This leads to highly glazed façades that are difficult to justify environmentally, from a solar heat gain and a heat loss point of view, but delightful to look through.

21.3.3 Heating

One of the basic attributes of a comfortable building in a cold climate is that it is warm in the winter. Heat energy is put into the building to maintain a thermal gradient between inside and out. The rate of heat loss is a function of the level of insulation in the external envelops and the volume of external air coming in that needs to be heated up. Increasing insulation standards will reduce the fabric heat loss, and making the building well sealed will reduce the amount of air that needs to be treated. Increasing the insulation levels of the external elements will also raise their internal surface temperature, and reduce the discomfort of a cold radiant surface and cold down drafts in the room.

The heat loss from the ventilation air can be further reduced by using the outgoing air to pre-heat the incoming fresh air. This is normally done in conjunction with a fan powered ventilation system to overcome the resistance of the heat exchanger, although wind powered versions are said to function.

As the lighting (both electrical and daylight), computers, IT equipment and the people themselves all give off heat, it is possible to see how the building could be warmed with little or no additional energy, particularly if it is recovering the heat from the outgoing air. If the internal heat gains are sufficient to warm it in the coldest periods, it must be overheating at all other times. If the heat gains exceed the losses for most of the time that the building is occupied, then the case for the added complexity and electrical fan power for heat recovery is difficult to justify.

21.3.4 Thermal storage

Ideally the excess heat should be stored for times when the heat loss exceeds the gains. This can be done in the surfaces (walls, floors, ceilings), furniture and loose fittings in the room. Driving heat into and out of the building fabric requires a swing in the room temperature. This is particularly true of phase change materials that have a few degrees of hysteresis. A tight environmental control brief will therefore make it very difficult to make use of the thermal mass as the room temperature may not be allowed to deviate sufficiently to drive the heat into the fabric. Ideally the thermal mass needs to be in the space, connected by radiation and convective heat transfer. Covering it with an insulation material will increase the thermal gradient required and consequently the swing required to make use of the thermal storage.

The thermal mass of a material is governed by its thermal conductivity, mass and specific heat capacity. The nature of storage is that it is cyclical. The longer the period of the cycle the further the heat can travel into a material and the greater the amount of heat can be stored. Analysis has shown that for dense material such as concrete, the amplitude of variation in temperature over a 24-hour cycle becomes small about 70 mm from the surface. The depth will increase over longer time scales. It is possible to use a remote heat store such as the ground, but some active mechanism is required to connect the mass with the space by moving air or water. Blowing air down the holes in pre-cast concrete panels that form the building slabs is a way of doing this. Thermodec sell this as a product.

21.3.5 Cooling

In hot climates the situation is reversed from heating in that one needs to limit the heat coming in and employ means of getting rid of the internal heat gains. Insulation helps in a similar manner in reducing the heat flux, as does minimising the external air infiltration when it is hotter outside. The colour of the external surfaces (albedo) will affect the amount of solar radiation absorbed and hence the temperature (white is cooler), which will in turn affect the heat transmitted into the space. Thermal mass can help by absorbing heat when it is hot and getting rid of it when it is cooler, and the hot surfaces can radiate heat to the sky at night.

Evaporation is one of the main forms of heat rejection in a cooling tower. Plants also keep cool by transpiration of water. Having a wet external surface in the form of a green planted roof or wall will keep the temperature of the surface down and reduce the heat gain if not do some active cooling.

The other aspect of hot climates is that the external air has a higher humidity than the desired internal level, and it cannot be used for dehumidification. The refrigeration load to dehumidify the air is often greater than the cooling load. One has to be careful of moisture coming in rather than going out. It is better for any transpiring planting to be on the outside rather than inside the occupied space where they would raise the humidity.

21.3.6 Ventilation

The ability of the fresh air to help condition a space depends on the climate. In most temperate climates it can be used for cooling and controlling humidity. As mentioned above, it is a manner of controlling the temperature in a well-insulated building that is heated with its internal gains. When it is hot or very humid there are other mechanisms for cooling deployed and the fresh air needs to be treated using energy, and the amount limited to the minimum.

The ventillation is often linked to the CO₂ level in the building as there is a direct correlation between that and the occupancy. 8 litres of fresh air per second per person (l/s/p) will equate to a CO₂ level of 1000 ppm and 3 l/s/p would be 1800 ppm. The correct amount of CO₂ in a room is the subject of some debate especially in schools. The UK schools guidance document Building Bulletin 101 sets out a regime that allows one to have a natural ventilation system that has a minimal ventilation rate for most of the time which can be increased to provide rapid purge ventilation.

Except in the case where the outside air is always the right temperature, the ventilation rate will need to be controlled. In a similar manner to daylight, the perimeter of the building can be opened to let in fresh air using wind pressure and the differences in buoyancy of the air. However, the wind and buoyancy forces to drive the process are highly variable. In the winter of a temperate climate, the buoyancy and wind forces are very high and the fresh air required is at its minimum. In the summer, very high volumes of air are required when the forces are very much lower. As such the openings need to be variable and controllable. This becomes more important as buildings are sealed up to reduce heat loss and one cannot rely on the background air permeability and infiltration rate. This is not a trivial design issue. The design needs to address:

By contrast, a mechanical fan assisted ventilation system will provide a controlled ventilation rate at a cost of the power needed to run the fan. The choice between natural ventilation and mechanical ventilation in many situations is a subtle one that depends on the ease of control and maintenance of the relative systems.

As a rule of thumb, a room with openings on one side can be ventilated about three storey heights deep. Single-sided ventilation is largely driven by buoyancy. Having openings on both sides of a building or connected to a shaft to the roof will increase the natural ventilation by making use of wind pressure variations around the building. A taller volume of air will create a greater buoyancy driven stack pressure as well.

21.3.7 Internal moisture and pollutant control

As well as regulating the heat loss and CO₂, ventilation controls the removal of internally generated water vapour and other pollutants. It is important to control the level of these to maintain a healthy environment in a building. This is on the basis that the external concentration of the moisture and other pollutants are lower than internally, so external air will dilute the internal concentration. This is not always the case when the outside is more humid or polluted and has to be treated to bring it to the comfort standards required internally.

It is possible for the gases to diffuse to outside though the fabric down a concentration gradient. However, permeability and the differences in concentrations are generally too small to make this the only form of pollutant control. Indeed, the offgassing of materials and the naturally occurring radon coming from the rocks in certain areas of the UK such as Cornwall and the Midlands, mean there is more diffusing in than out. Having said that, moisture can diffuse through fabric and cause problems by condensing on cold elements in the construction if it is not controlled or allowed to escape. Generally speaking, the humidity levels in a building should be kept well below 70% to prevent mould growth. Surface areas of high heat loss without a compensating heat source are areas where the room air can cool down, increasing the relative humidity and risking condensation. Well-sealed buildings with carefully controlled ventilation rates will have higher internal humidities. This is not such a risk if there is a commensurate increase in the levels of insulation such that the internal surfaces are warmer. However, this situation will be less forgiving of any ‘cold bridging’ areas of poor insulation that will result in pockets of high heat loss and high surface humidity (Fig. 21.2).

Like heat, the moisture production in a building is not continuous and depends on the number of occupants, cooking and bathing activities. Absorbent materials will act like sponges to take up the moisture from the air when the concentration is high and release it over time when the moisture producing activity has ceased. This buffering is useful in preventing peaks of high humidity in the space, providing there is a time of low humidity when the material can dry out.

Desiccants are very good at absorbing moisture from the air at low temperatures and releasing it at high temperatures. This is useful in active systems to remove humidity from the air and using heat to dry and regenerate the material.

21.3.8 Energy usage in buildings

Energy is used in a building to provide heating, cooling, light, hot water, to pump air and water, and to drive appliances. The amounts vary according to the usage, climate and overall efficiency of the building. Traditionally the greatest energy usage in temperate climates has been the space heating. In hot climates this is replaced with the cooling. The amount of fan and pump power depends on the types of heating, cooling and ventilation systems used. The lighting load will depend on the building usage. However, it is the electrical demand of gadgets and IT that is increasing at a fast pace which generally the designer has no control over (Figs 21.3 and 21.4).

21.4.1 Client brief: environmental control standards and maintenance

As discussed above, tight environmental control standards are possible but generally require energy to achieve. Wider limits on temperature, light levels, noise, air flow, etc., allow greater possibilities for the use of passive control. The extent to which the occupants are prepared to adjust their environment by operating blinds, opening windows, and the maintenance that arises from the materials and equipment used needs to be agreed. This will ensure that the conditions and the maintenance of the building, when delivered 2 to 4 years later, is not a surprise. Avoiding an unhappy client or user should be one of the main aims of the design process, and early dialogue on these issues is essential.

21.4.2 Fitting into the existing urban fabric

The building should be fitting into the surrounding fabric in terms of the height and massing generally. In areas of historic interest there may well be restrictions on the changes one can make to the external appearance of the building and to the historic building fabric itself. This can put considerable limitations on energy saving techniques to do with insulation. It is a challenge for new materials to make historic buildings more energy efficient and maintain their character.

Planning issues must be taken into account when considering large developments. Fundamentally the density of development will determine how far apart destinations such as schools, parks, shops, places of work, etc., are from each other, and how viable sustainable transport systems will be. Low density suburban developments have built up with a reliance on the car to provide convenient transport. The distances are too big to walk or cycle, and public transport will not have the custom to make it profitable. At higher densities, walking and cycling becomes possible and public transport becomes viable to provide frequent and convenient services. The density does not have to be like the towers of Hong Kong for this to work. London has terraces of buildings that are two to six storeys high that supports a good transport system.

As well as the density, the arrangement of spaces needs to be considered to make a development pleasant. How far one is from a school, shop, park, museum, zoo, health centre, hospital will differ and should be considered against how frequently they are used and the mobility of the users. Keeping the streets animated at all times of the day and evening with different activities will help keep the vibrancy of the space. Creating spaces that people want to be in and go to is arguably more important now than it has been in the past because technology has removed the requirement to move from one’s dwelling at all. The basics of working, shopping, and entertainment can be done at home with increasing perfection as modern information technology gets better and better. This is not good for social cohesion.

21.4.3 Climate and site conditions: noise, sun path, pollution, wind and dust

Information concerning climate, sun path, wind, external noise and air pollution needs to be considered to identify the potentials for passive design measures and avoiding unwanted energy loads. The climate will dictate what systems need to be put in place (heating, cooling, etc.) and when it is possible to use natural ventilation. External sources of noise, dust and pollution will create challenges to using natural ventilation. The overall light levels and sun path will inform the extent to which daylight can be used as a resource for heating and lighting and conversley needs to be avoided because of overheating and glare. Prevailing wind direction and forces will equally determine how much of this resource can be used to drive ventilation or needs to be controlled to avoid discomfort.

21.4.4 Design

From these constraints one can devise ways to set out the massing of the building in terms of its orientation, height and surface area to volume. Generally, thinner building plans are easier to light and ventilate naturally than thicker ones, but deeper plan floor plates are more economic and provide bigger, more useful floor areas. Light shafts, atria and courtyards can be used to break up an otherwise deep plan building.

This needs to be looked at in conjunction with the other aspects such as the usage patterns, insulation and the thermal mass of the building and how the active conditioning systems (heating, ventilation, lighting, etc.) work. It is all too easy for the active systems not to take advantage of, or indeed work against, the passive systems if they are not thought about and set up correctly.

For example, in a temperate climate, one could insulate a building sufficiently well such that the internal gains meet the heat losses. The thermal mass will buffer the heat gains so they can be used later. In the summer the windows can open and the thermal mass can be used to store excess heat in the day and discharge it at night. Another example is an apartment in a tropical climate occupied mainly at night, which is likely to want cooling for a few hours in the evening. In this case, thermal mass that may store the heat gain through the day when the space is empty would be counterproductive. Lightweight finishes would be able to be cooled down quickly with the active cooling system. There are a number of computer tools that will model how the building will perform (for example, Ecotect, Energy Plus and IES). While these are useful to test one’s ideas, they will not produce the design idea.

21.4.5 Documentation and delivery

The design needs to be documented in such a way that it will survive the designer who may not be employed to see the system through. This is particularly true for new techniques to the industry or designs that cross conventional demarcation lines. The airtightness of a building fabric is an area that involves many different parties. Getting a window actuator to open on a command from the building management computer and the fire alarm panel requires the coordination of a number of designers, suppliers and contractors. The designer needs to consider the expertise of not only the operatives but the procurement team. Ideally the designer should be involved to see the project through but this is not always possible.

21.6.1 The drivers for more sustainable buildings

Generally there are several drivers that can be used to get better buildings. The government is in control of some of them but the market and customer choice are also drivers.

The legislation determines minimum standards of building performance. In the UK this is in the planning system and the building regulations. There is an onus on the designer to show that the building design complies and the construction is air tested to prove the fabric permeability rates. However, the ongoing actual performance of the building is not captured in this approach.

Enforcing labelling the energy use of buildings is the next aspect of legislation. The hope is that the market will choose better building if they have the information, just as they would choose a refrigerator. There are other voluntary auditing schemes that cover a whole range of sustainable issues. BREEAM is a UK version, LEED is in the US, Greenstar is an Australian version, and ESTIDAMA is being developed in the United Arab Emirates.

The corporate social responsibility agenda of organisations is driving change in companies. At worst it is a publicity exercise that is intended to cover some other corporate sins. At best it is a way of refocusing the business in a positive manner and achieving better profit through using fewer resources, producing less waste and having happier people involved with the company. Better companies are instituting auditing processes to address these issues.

The final lever is the cost of energy, water and any other resource. Clearly the more expensive the resource the greater the incentive to use less. This is manipulated by government taxation, but the market price of energy is a global commodity, can be volatile and present a cost risk to a consumer that is not of the government’s making.

There is a risk that these drivers may miss the issues that are not measured directly like comfort and health. Adding draft stripping without adequate alternative measures of ventilation or humidity control could reduce the requirement for heating but create health problems for the occupants.

21.6.2 The brief for new materials

Any new product should have a particular need that it fulfils. However, it needs to be accompanied with the design tools to enable designers to be able to characterise the product performance. Integration with the other elements around it needs to be resolved to avoid the interface issues and it needs to be sufficiently robust to work in a building. It has also got to be possible to build it using the skill set that is currently available or could easily be developed.

Materials tend to be thought of as passive elements of buildings. They perform various functions such as supporting, insulating and making the building weather tight. They also act to buffer the temperature and humidity in a space. New material would do these tasks ‘better’. ‘Better’ in this context has a number of meanings such as easier to install, more robust, taking up less space. This would be especially the case when trying to upgrade an existing building with the occupants in situ. Another definition of ‘better’ would be one that uses fewer resources, and damages the environment less in its manufacture, installation or disposal.

Often there are a number of functions needed from a façade or a building surface. Concrete is a good structural material and thermally massive. However, it is not acoustically absorbent and is not a good moisture buffer. Rooms with concrete soffits may stay cool but the acoustics and moisture may be a problem. A material that combined thermal mass, moisture buffering, acoustic absorption but reflected light would be a useful addition.

21.6.3 Dynamic materials

Materials would be more useful if they had a variable or active component to them. As has been said above, there is an aim to get the need for heating down by insulating the buildings to a greater extent so that the internal gains are enough to meet the heat loss in the winter. This means that the building will overheat for most of the time. If the fabric could vary its insulation value, it could manage the heat loss to keep the internal conditions stable. The same could be said of the transparency for light and solar energy, and the management and filtering of air movement though the façade. These are all functions that can be done with windows, shutters, blinds and electrochromatic glass, but there may be ‘better’ ways of doing this. ‘Better’ would include being automatically controlled and self-actuated.

It might be posible for more active materials to self-clean, heal and selfassemble. Ultimately they could be used to alter the environment rather than simply buffer variations. This would mean the materials taking over the jobs of the machines, or blurring the distinction between the two. That is providing heating, cooling and lighting in the space. The external façades of buildings could be used for heat rejection and we have seen light emitting materials. Any process that uses energy will ultimately produce heat to offset heat loss. Managing the gas transfer could be done by altering the porosity of the external façade with small enough gaps to filter the air. Alternatively the gas transfer could be done selectively, moving the products of respiration (water vapour and CO₂) and any other pollutants out, and oxygen in while leaving the levels of inert nitrogen the same inside and out. These active processes will require energy and a complete system would collect its own from the sun and wind around the buildings.

21.6.4 The living world

The systems described in the previous section describe the living world where all these functions are present. There is environmental control, selfassembly, energy collection, storage and distribution. The materials are all recyclable. The systems are finely tuned and very sophisticated. The roots of a tree use a comparatively small amount of material compared to conventional foundations and piles. One cannot help notice that the trees are left standing after an earthquake has levelled the buildings around. The living world has structure, insulation, gas transfer, movement and even bioluminescence. The greatest challenge is to harness these technologies and engineer them more directly for our own use.

The relationship between plants and buildings has been that they are best kept apart as one tends to damage the other. We are used to using dead products such as wood or leather but not living ones (Fig. 21.11). This could start with using plants for shading or cooling the external façade of the building. In temperate climates a deciduous plant will drop its leaves in the winter and allow more heat and light in than in the summer when the leaves are out. Where it will end is more in the hands of genetic engineers and cancer researchers as much as the material scientist of today.

21.7 Sources of further information and advice

Alexandri, E., Jones, P. Temperature decreases in an urban canyon due to green walls and green roofs in diverse climates. Building and Environment. 2008; 43(4):480–493.

Anon. (a) Website produced by Strathclyde University. Available at: http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/hec.htm, August 2009. [accessed].

Anon. (b) UK Environment agency guidance on the benefits of green roofs. Available at http://www.environment-agency.gov.uk/business/sectors/91970.aspx, August 2009. [accessed].

Bouchlaghem, K., Nsom, B., Latrache, N., Haj Kacem, H. Impact of Saharan dust on PM10 concentration in the Mediterranean Tunisian coasts. Atmospheric Research. 2009; 92(4):531–539.

Building Bulletin 93Acoustic Design of Schools, A Design Guide. UK: Department for Education and Skills, 2003.

Building Bulletin 101Ventilation of School Buildings. Department for Children, Schools and Families, UK Version, July 2006. [1.4, 5].

DEFRA. UK government statistics. Available at: http://www.defra.gov.uk/sustainable/government/progress/national/16.htm, August 2009. [accessed].

DEFRA. Accounting for the Effects of Climate Change, June 2009. Supplementary Green Book Guidance. Produced by HM Treasury and Department for Environment Food and Rural Affairs. Available at http://www.defra.gov.uk/environment/climatechange/adapt/pdf/adaptation-guidance.pdf, August 2009. [accessed].

Loh, M., Coghlan, P. Domestic Water Use Study in Perth, Western Australia, 1998–2001. Available at http://www.energyrating.gov.au/library/pubs/wa-wateruse.pdf, 2003. [(accessed August 2009).].

MacKay, D. Sustainable Energy – Without the Hot Air. Available at http://www.withouthotair.com/, 2008. [(accessed August 2009).].

McKinsey Global Institute. The Carbon Productivity Challenge: Curbing Climate Change and Sustaining Economic Growth, Page 14, Exhibit 5. Available at: http://www.mckinsey.com/mgi/publications/Carbon_Productivity/index.asp, 2008. [(accessed June 2009)].

National Atmospheric Emissions Inventory, UK. Available at: http://www.naei.org.uk/pollutantdetail.php?poll_id=24&issue_id=1, http://www.naei.org.uk/pollutantdetail.php?poll_id=24 (accessed July 2009).

Regional Air Pollution in Developing Countries, Sweden. Available at: http://www.sei.se/rapidc/emissions.htm (accessed June 2009).

Statutory Instrument 1989 No. 1790, The Noise at Work Regulations 1989. Available at: http://www.opsi.gov.uk/si/si1989/Uksi_19891790_en_1.htm (accessed June 2009).

US DOE Buildings Energy Data Book: 1.1 Buildings Sector Energy Consumption Section 1.1.3 Buildings Share of U.S. Primary Energy Consumption (Percent). Available at: http://buildingsdatabook.eren.doe.gov/docs/xls_pdf/1.1.3.xls (accessed August 2009).

US EPA website on air pollution. Available at: http://www.epa.gov/air/airtrends/aqtrnd95/pm10.html (accessed July 2009).

Wikipedia (a) Article about Prius car. available at: http://en.wikipedia.org/wiki/Toyota_Prius#EV_mode (accessed August 2009).